Cutting tools

ABSTRACT

A cutting tool comprising a cutting bit, a tool holder having a cutting bit receiving recess and a clamping member for clamping the cutting bit in the recess of the tool holder. The flank surface of the cutting bit remote from its cutting edge has two recesses therein, the bottom surfaces of which extend inwardly of the cutting bit at an acute angle with respect to a lower, seating face of the cutting bit. Two toe dogs are provided on the clamping member and engage in the recesses of the cutting bit with flat contact with the bottom surfaces of the recesses to position the cutting bit in the cutting bit receiving recess.

The present invention relates to cutting tools and particularly tocutting bits and toolholders for holding the cutting bits.

German Pat. No. 1,293,525 discloses a cutting tool comprising a cuttingbit which is clamped into a recess provided on the front of the holder.The bit consists of a hard cutting material, especially if it is to beused for heavy cutting, and has, in vertical section, a rhombus-likecross-sectional shape, a stepped recess being provided in the rearcontact face of the cutting bit for receiving a clamping strap or memberwhich is inserted from the cutting side. The clamping member can bereset and fixed in the recess of the holder by means of a fasteningscrew passing through an elongate slot in the member and also provides asupport for the back of the cutting bit.

In this known cutting tool, the stepped recess in the rear contact faceof the cutting bit extends over the entire width of the latter. Thebottom face of this recess runs parallel to the seating face of thecutting bit. When tightening the clamping strap, it is thereforenecessary for the operator always to take particular care that the backof the cutting bit makes full contact with the clamping member otherwisedependable tightening of the cutting bit will not be obtained.

According to one aspect of the present invention there is provided acutting bit having a rhombus-like vertical cross-sectional shape andcomprising upper and lower spaced-apart faces and flank surfacesextending between the upper and lower faces, a cutting edge formed bythe junction of the upper face and one of the flank surfaces, and tworecesses which open into another of the flank surfaces remote from theone flank surface, the bottom surfaces of the recesses extendinginwardly from the other flank surface at an acute angle to the lowerface.

According to another aspect of the present invention there is provided aclamping member for clamping a cutting bit having two recesses in aflank surface remote from the cutting edge, in a recess of a toolholder,the clamping member having two toe dogs which in use engage in therecesses in the cutting bit to hold the bit in position as the clampingmember is secured to the toolholder.

According to a further aspect of the present invention there is provideda cutting tool comprising a cutting bit, a toolholder having a cuttingbit receiving recess therein and a clamping member for clamping thecutting bit in the recess; the cutting bit having a rhombus-likevertical cross-sectional shape and comprising, upper and lowerspaced-apart faces and flank surfaces extending between the upper andlower faces, a cutting edge formed by the junction of the upper face andone of the flank surfaces, and two recesses which open in another of theflank surfaces remote from the one flank surface, the bottom surfaces ofthe recesses extending inwardly from the another flank surface at anacute angle to the lower face; and the clamping member having two toedogs engaging in the recesses and adapted to make flat contact with thebottom surfaces of the recesses to position the cutting bit in thecutting bit receiving recess.

The provision of two recesses which are open only towards the rearcontact surface and optionally to the tool face of the cutting bitresults in positive locking of the cutting bit, even under the effectthereon of component forces which point neither in the direction of theback-pressure acting on the cutting edge of the bit nor the direction ofthe main cutting pressure acting on the cutting bit. This is ofparticular advantage when there is no additional lateral support for thecutting bit in the recess of the holder. Furthermore, the provision ofonly two recesses of relatively small volume in the region of the rearcontact face of the cutting bit results in a minimum of weakening of thecutting bit's own strength, so that the latter fulfils its purpose, whenused for heavy cutting, in an optimum manner. The slope of the bottomfaces of the recesses in the direction dipping into the cutting bitresults in a dove-tail-like cross-sectional shape of the regions of thecutting bit which are in direct contact with the doe dogs of theclamping strap, so that, when the toe dogs of the clamping strap aretightened, the cutting bit is not only drawn in the direction towardsthe bottom of the recess of the holder, but is also drawn backwards inthe direction towards the clamping strap.

The bottom faces of the recesses may be mutually inclined in thelongitudinal direction of the rear contact face of the cutting bit toprovide for addtional locking of the cutting bit against lateral shift,say in the direction of the main cutting edge of the bit.

The side faces of the recesses may approximately have a part-cylindricalshaped surface and, correspondingly, the toe dogs of the clamping membermay have the outline shape of a sector of a cylinder, with the cylinderaxes perpendicular to the bottom faces of the recesses. The provision ofsuch recesses ensures that weakening of the cross-section of the cuttingbit by the recesses is extremely slight.

A spline-like projection may be provided on the underside of theclamping member, which projection serves to increase the strength of theregion which is particularly stressed by the fastening screw whichpasses through an elongate slot extending longitudinally of the clampingmember. Thus, the spline-like projection may be regarded as forming thespine of the clamping member. The spline-like projection may include adownwardly extending extension at an end opposite the end facing thecutting bit. The extension ensures that the bottom of the clampingmember and the bottom of the spline-like projection, away from theextension, are free with respect to the bottom of the recess in theholder and, when the fastening screw passing through the slot istightened, the surface of the extension thus acts, in a manner ofspeaking, as a swivel bearing for the motion of the clamping member.This motion then is a rotatory motion which is particularly favourablefor reliable tightening.

A groove may be provided in the bottom of the recess of the toolholderinto which the spline-like projection is slidably movable. With such anarrangement the spline-like projection simultaneously serves for guidingpurposes and for locking the clamping member against lateral shift. Suchlocking is of particular advantage when the cutting tool is used for aneck turning tool.

Alternatively the recess in the toolholder may have a lateral wall aswell as end wall and a planar bottom so that the cutting bit and theclamping member can be used without altering their shape, not only forneck turning tools, but also for roughing tools. When the clampingmember is used in such a roughing tool, the extension of the spline-likeprojection sits on the bottom of the recess on the holder. This seatingof the clamping member which in a manner of speaking is pointlike,enables the clamping member to be mounted in such a way that it can movenot only in the direction of its central longitudinal plane, but alsotransversely thereto, so that it can follow the particular geometricalfeatures at the holder and at the cutting bit in an optimum manner, inthe sense that as far as possible over-rigid tightening of the cuttingbit is avoided.

The present invention will now be described, by way of example, withreference to the accompanying drawings, wherein:

FIG. 1 shows a vertical section through a portion of a neck turningtool, along the line I--I of FIG. 2;

FIG. 2 shows a plan view on the neck turning tool shown in FIG. 1,viewed in the direction of the arrow II;

FIG. 3 shows a section along the line III--III in FIG. 2;

FIG. 4 is a vertical section through a roughing tool along the lineIV--IV of FIG. 5;

FIG. 5 is a plan view of the front part of the roughing tool shown inFIG. 4, as viewed in the direction indicated by the arrow V in FIG. 4;

FIG. 6 shows a plan view of a roughing tool which, in contrast to FIG.5, is a left-hand cutting tool as opposed to a right-hand cutting tool;

FIG. 7 shows a front elevational view of the roughing tool as viewed inthe direction of the arrow VII of FIG. 6;

FIG. 8 is an elevation view of the clamping strap or member;

FIG. 9 is a front view of the clamping member shown in FIG. 8 as viewedin the direction of the arrow IX in FIG. 8;

FIG. 10 is a plan view of the clamping member shown in FIG. 8, as viewedin the direction of the arrow X in FIG. 8;

FIG. 11 is a section on the line XI--XI in FIG. 10;

FIG. 12 is a rear elevational view of a cutting bit as viewed in thedirection of the arrow XII in FIG. 13;

FIG. 13 shows a vertical section along the line XIII--XIII of FIG. 14,and

FIG. 14 shows a plan view on the cutting face of the cutting bit asviewed in the direction of the arrow XIV in FIG. 13.

Referring initially to FIGS. 1 to 3, there is a frontal opening orrecess 2 in the holder at the front end of the holder shank 1 on theneck turning tool. A clamping member 3 and a cutting bit 4 are locatedinside the recess 2 on the holder. The cutting bit 4 consists of a hardcutting material, for example sintered carbide. The illustrated cuttingtool which is clamped in position on a machine, such as a lathe isintended particularly for use in heavy cutting.

The cutting bit 4 has a rhombus-like cross-sectional shape (FIG. 13).The tip of the rhombus which forms a main cutting edge 5 is designatedas 6. The cutting edge 5 is formed by a top or tool face 7 and a flankor side face 8.

Two stepped recesses 10 are provided in a rear contact face 9 of thecutting bit 4. The two transversely separated recesses 10 are providedin the cutting bit 4. Their positions are symmetrical to the verticalcentral longitudinal plane 11 of the cutting bit 4 and the clampingmember 3. The recesses 10 are open towards the tool face 7 and the rearcontact face 9 of the cutting bit 4. The bottom faces 12 of the recesses10 form an acute angle 14 with the bottom or seating face 13 of thecutting bit, which angle converges in the direction interiorly of thecutting bit 4. The bottom faces 12 of the recesses 10 are mutuallyinclined not only in the direction XIV (FIG. 13) dipping into the recess10, but also in the longitudinal direction 15 of the rear contact face 9(FIG. 12). The bottom faces 12 therefore form an obtuse angle 16 withone another, which opens towards the seating face 13 of the cutting bit.

The clamping member 3 has a front contact face 17 which supports thearea of the rear contact face 9 of the cutting bit 4. For this purpose,the front contact face 17 of the clamping member 3 is inclined at anangle corresponding to the inclination of the rear contact face 9 of thecutting bit 4. The toe dogs 18, 19 protrude from the contact face 17.The rearward extending upper faces 20 of the toe dogs 18, 19 and theupper front face 21, adjacent thereto, of the clamping member 3 have aconcave shape to serve as chip deflection surfaces. The front face 21 ofthe clamping member 3 extends upwards beyond the toe dogs 18, 19. Thepressure-applying surfaces 22 of the toe dogs 18, 19 are aligned so thatthey rest in a plane-parallel manner on the bottom faces 12 of therecesses 10 of the cutting bit 4, when the clamping member 3 istightened.

The side faces 23 of the recesses 10 have an approximatelypart-cylindrical shape. Accordingly, the toe dogs 18, 19 also areprovided with a part-cylindrical outline shape 24 which, however, has acylinder diameter smaller than that of the part-cylindrical recesses 10.The axes 25 of the cylinder shape of the side faces 23 of the recesses10 are perpendicular to the abutting edges 26 formed by the junctions ofthe bottom faces 12 of the recesses 10 with the rear contact face 9 ofthe cutting bit 4 and, also are perpendicular to the bottom faces 12.

The bottom 27 of the clamping member 3 is provided with a spline-likeprojection 28. The projection 28 extends in the direction of an elongateslot 29, the longitudinal axis of which lies in the central longitudinalplane 11 of the clamping member 3 and extends from top to bottom throughthe clamping member and through the projection 28. The spline-likeprojection 28 also extends symmetrically to the central longitudinalplane 11, in the longitudinal direction of the latter. The spline-likeprojection 28 has a width 30 which is larger than the width 31 of theelongate slot 29. The central longitudinal axis of the elongate slot 29also lies in the central longitudinal plane 11. The toe dogs 18, 19 arealso arranged symmetrically one on either side of the centrallongitudinal plane 11. The end of the elongate slot 29, facing the uppersurface 32, is widened in such a way that a shoulder 33 is formed forreceiving a head 34 (FIG. 1) of a fastening screw 35. The shaft of thefastening screw 35 goes through the elongate slot 29 and engages with athread in the holder 1. This thread is cut internally into a bush 36which extends through the holder 1, transversely to the axis of thefastening screw 35 and is provided, transversely to its longitudinalaxis 37, with a threaded bore for screwing in the thread of thefastening screw 35. If the fastening thread for the screw 35 isstripped, the bush 36 with the internal thread can be replaced in thisway. Complete replacement of the holder 1 is not necessary.

An end 38 of the spline-like projection 28, facing away from the cuttingbit 4, is provided with a downwardly protruding extension 39. In thecase of a neck turning tool, the spline-like projection 28 rests in aguide groove 40, which extends in the resetting direction 43 (FIG. 1) inthe bottom of the recess 2 on the holder. The central longitudinal planeof the guide groove 40 is identical to the central longitudinal plane11. The bottom 27 of the clamping member 3 is spaced by a distance 41from the bottom 42 of the recesss on the holder. The spline-likeprojection 28 makes contact with the bottom 44 of the guide groove 40only through the extension 39.

In the embodiments of the roughing tools shown in FIGS. 4 to 7, therecess 2 on the holder has a lateral contact face 45. The bottom 42 ofthe recess 2 on the holder is planar throughout. The area of the rearface 46 of the clamping member 3 is supported against the holder 1, ifnecessary, with the insertion of spacers (not shown). The fasteningscrew 35, the principle of fastening the fastening screw 35, theclamping member 3 and the cuttinhg bit 4 are, for the embodiment of theleft-hand cutting or right-hand cutting roughing tool (FIGS. 4 to 7),identical to the embodiments previously described with reference to theother figures. To enable the cutting bit 4 to be used either as a neckturning tool or as a roughing tool, the flanks 47, 48 of the cuttingbit, adjacent to the flank 8 of the main cutting edge 5, make an acuteangle 49, which converges in a direction opposite to the direction ofthe arrow 43, that is to say in the direction towards the rear end ofthe holder 1, with the flank 8 of the main cutting edge 5.

Inside the recess 2 of the holder, the cutting bit 4 rests on thesurface of a shim 50 which is replaceably mounted on the holder 1. Theupper face 51 of the shim 50 is at a level higher than that of thebottom 42 of the recess 2 of the holder.

I claim:
 1. In a cutting tool including a tool holder; means defining afrontal opening in the tool holder; a cutting bit accommodated in thefrontal opening of the tool holder and having a rhombus-like verticalcross-sectional shape, as well as a seating face, a tool face and a rearcontact face; a clamping member having a frontal contact face being inengagement with the cutting bit; means defining an elongated opening inthe clamping member; and a fastening screw passing through the elongatedopening and threadedly received in the tool holder for adjustablytightening the clamping member to the tool holder whereby the cuttingbit is clamped by the clamping member in the frontal opening of the toolholder; the inmprovement comprising means defining two spaced recessesin said rear contact face of said cutting bit; each recess being opentowards said rear contact face; each recess having a bottom faceinclining at an acute angle towards said seating face; the direction ofinclination of the bottom faces being oriented inwardly of said cuttingbit from said rear contact face; and two spaced toe dogs forming part ofsaid clamping member and being arranged at said frontal contact face ofsaid clamping member, said toe dogs being in a face-to-face contact withthe bottom faces in said recesses of said cutting bit.
 2. A cutting toolas defined in claim 1, wherein said recesses are open towards said toolface of said cutting bit.
 3. A cutting tool as defined in claim 1,wherein each said recess has a concave side face of the configuration ofa partial cylinder, said partial cylinder having a cylinder axis beingperpendicular to the bottom face of the respective recess; each said toedog having a convex outline of the configuration of a partial cylinder;the convex outline of each said toe dog substantially conforming to theconcave side face of the respective recess in said cutting bit.
 4. Acutting tool as defined in claim 1, wherein said frontal opening of saidtool holder has a rear wall and said clamping member has a rear facebeing in a face-to-face contact with said rear wall.
 5. A cutting toolas defined in claim 1, wherein said frontal opening of said tool holderhas a rear wall and said clamping member has a rear face being in aface-to-face engagement with said rear wall with the interposition of atleast one spacer member.
 6. A cutting tool as defined in claim 1,wherein said cutting bit further has a side face defining, with saidtool face, the main cutting edge of the cutting bit; and two flank faceseach bounding said side face; each said flank face being arranged at anacute angle with respect to said side face.
 7. A cutting tool as definedin claim 1, wherein each toe dog has a rearward extending upper face andsaid clamping member has an upper front face adjoining the upper facesof said toe dogs; said upper faces of said toe dogs and said upper frontface of said clamping member having a concave configuration toconstitute chip deflecting surfaces; said upper front face of saidclamping member extending upwards beyond said toe dogs.
 8. A cutting bitas defined in claim 1, wherein said bottom faces of the recesses aremutually inclined in the longitudinal direction of said rear contactface.
 9. A cutting bit as defined in claim 8, wherein said bottom facesof said recesses are inclined at an obtuse angle with the respect toeach other in the longitudinal direction of said rear contact face, saidobtuse angle opening in a direction towards said seating face of thecutting bit.
 10. A cutting tool as defined in claim 1, furthercomprising a spline-like projection provided on an underside of saidclamping member and extending parallel to said elongated opening andwherein said spline-like projection is located symmetrically to acentral longitudinal plane of said clamping member in the longitudinaldirection of the latter; said spline-like projection being wider thanthe width of said elongated opening; said elongated opening having acentral longitudinal axis lying in said central longitudinal plane andsaid toe dogs being symmetrically arranged on either side of saidcentral longitudinal plane.
 11. A cutting tool as defined in claim 10,further comprising a downwardly protruding extension of said spline-likeprojection at an end of said clamping member remote from said frontalcontact face from which said toe dogs project.
 12. A cutting tool asdefined in claim 10; said frontal opening of said tool holder having abase; further comprising a guide groove provided in said base andextending in a resetting direction of said cutting bit; said spline-likeprojection being located in said guide groove.
 13. A cutting tool asdefined in claim 12, further comprising a downwardly protrudingextension of said spline-like projection at an end of said clampingmember remote from said frontal contact face from which said toe dogsproject; said spline-like projection being in contact with a bottom ofsaid guide groove solely by means of said extension for providing aspace between the underside of said clamping member and the base of saidfrontal opening.
 14. A cutting tool as defined in claim 1, wherein saidfrontal opening of said tool holder has a lateral contact surface and abase which is planar throughout.